Chapter VIII: Part II: Materials Employed in Horology (4)

On a small open frame C C, fig. 46, fix several parallel bars _f l_, _e d_, etc., and on two of these adjust a slide _p o n m_, with two strips glued underneath so that it can travel up and down between _a_ and _b_. On _p o n m_, fix a guide of convenient form, as G; and, after cementing the piece, say A, that is to be watered on a board resting on the bench, place the frame C C above it and trace the figure of the guide with a pegwood stick charged with polishing material. The same figure can be reproduced in parallel rows as the guide can be moved up or down.

By varying the shape and position of the guides, the water lines can take the form of waves, festoons, circles or ovals. In the two latter cases the guide has apertures of the requisite form, and the board that carries A, not being more than half the size of the aperture, can be moved about by hand or by a tool.

If preferred, one of the bars, as _e d_, can be graduated and arrangements can be made for clamping the slide by screws in any position.

These explanations will suffice to enable any intelligent watchmaker, after a few trials, to imitate successfully any of the beautiful watered surfaces that are, on a manufacturing scale, produced by machinery.

As regards the material to be used, first mix medium rouge and putty powder in equal proportions. It will be possible to decide from the shade obtained whether more putty powder should be added, because when there is too much rouge, the surface does not acquire a good white color.

POLISHING.

=181.= =To polish brass.= When it is required that a surface be maintained perfectly flat, first dress with somewhat coarse water of Ayr with blue stone and then go over with a softer stone. Next work with fine rottenstone and oil on a felt or buffstick for objects of large dimensions and on a piece of pegwood for smaller articles. They are then soaped, washed and dried in sawdust (=151=).

The work can be accomplished more rapidly, but without maintaining a perfectly flat surface, by first employing pumice-stone and oil spread over a large piece of soft wood or felt. It is then cleaned and polished with rottenstone.

When the form permits of it, a tin disc charged with tripoli and rotating in a lathe can be employed.

_Observations._ Pumice-stone is powdered fine and then sifted. In using rottenstone a piece an inch or two cube is crushed between the fingers into a cup of water, and this is decanted so as to give several degrees of fineness (=168=). The polishing can best be effected by using old wood from which the sap has dried up: French chalk has but little action if the polisher with which it is applied is from the animal kingdom, horn for example, etc.

=182.= =To polish watch wheels.= Although the operation of polishing is extremely simple, it is very important that a certain degree of manual skill be acquired by practice, as otherwise the work is never of the best.

We will here enumerate several methods of procedure, in order that, after trial, each can select the method with which he finds himself most successful.

_Smoothing._ The smoothing should be done carefully with very soft water of Ayr stone, free from veins and hard grains and perfectly flat. The wheel must then be well cleaned.

_Polishing._ In polishing, rods of walnut or boxwood, of tin, bronze or zinc are used. A buffstick and burnisher are also employed.

The materials applicable are rottenstone (with oil or alcohol, being made very thin in the latter case) tripoli, prepared chalk, polishing rouge, crocus, etc. These materials have been sufficiently described in articles =165-7.= Workmen sometimes prefer to make mixtures of two or more substances, but it is more usual to employ them separately.

=183.= _First Method._ After smoothing and cleaning the wheel, it is polished while resting on a piece of cork, where it is held between the fingers which cause it to rotate; the best rottenstone is used and is applied by smooth pieces of boxwood, about 8 inches long, which are filed to a bevel edge. It is best to have the grain of the wood crosswise and the polishers should be of sufficient thickness to prevent their bending when in use.

The rottenstone can be replaced by tripoli and the boxwood by walnut. Some wheel polishers prefer a triangular stick of pure tin or zinc which is often planed to ensure perfect flatness; rouge, rottenstone or tripoli can be used with it.

The wheel, after being well washed in soap and hot water, is thoroughly dried and finished with a fine buffstick in good condition, while it rests on a cork covered with smooth felt; this operation is with a view to prepare the surface prior to using the burnisher.

Some polishers, instead of the dry buffstick, prefer one charged with a little rouge, tripoli or rottenstone moistened. But such preparations must be applied very sparingly as they involve a risk of rounding the edges.

The burnisher is next rapidly passed over the surface of the wheel, which rests on cork, covered with a linen rag, or on a piece of wood, covered with smooth paper. Some give long backward and forward strokes with the tool; others give semicircular movements. It will be found sufficient to give short strokes from half an inch to an inch in length. A slight motion of the wrist is all that is required and after a few trials the necessary skill will be attained. We cannot say more. Practice must also be relied on for determining the most suitable pressure.

The burnisher, about half an inch wide and four inches long, is curved in the direction of its length. A straight burnisher might be used, but it is less safe; the angle of the burnisher set against the pinion should be rounded off.

The burnisher is cleaned and restored by drawing across a large flat piece of walnut charged with rouge of very good quality and very pure. After being washed, a little white wax is passed over it, and then it is again rubbed vigorously with a piece of cloth or a buffstick; finally with a soft linen rag. When a tendency to stick shows itself this operation must be repeated.

=184.= _Second process._ By this method the surfaces are somewhat rounded off at the edges. But, although not so pleasing to the eye, this circumstance involves no inconvenience except that, when burnishing, the burnisher would not at once come in contact with the entire surface; we need not, however, employ the burnisher.

Laying the wheel on a cork, some workmen smooth the wheel by covering it with oil and fine tripoli and rubbing with a walnut-wood stick. Others spread a layer of such a mixture first on the stick and then rub the wheel. When no more lines are observable across the surface of the wheel it is cleaned, placed on a fresh cork that is covered with a soft linen rag, and polished with a fresh buff stick (or one that has already been used for a similar purpose) and an abundant supply of rouge or even fine rottenstone and oil may be used. The buffstick receives a semicircular movement in all directions in order not to needlessly round the corners, the edges of the teeth and the crossings.

It is then washed in warm water, bathed in alcohol and dried with a fine linen rag.

=185.= _Third process._ After smoothing with a very soft stone, rub it with a piece of the root of boxwood cut across the fibre, on which is a layer of the following composition:

Two-thirds rottenstone mixed with one-third castile soap, worked into a paste with a few drops of water so that, although not a liquid, it can be spread out at will.

Make the wheel move backwards and forwards between the fingers while resting on a smooth, good cork, without a linen rag, and, as the operation nears its completion, a semicircular motion should be given to the wood. Wash with soap, boil in alcohol and dry.

The wheel can be burnished on a cork without any linen rag and the (curved) burnisher should be moved with short circular strokes from the center towards the circumference, gradually working up towards to the extremity of the burnisher; the same portion of the burnisher should not pass twice over the wheel (see also article =166=). For common work, fairly satisfactory results may be obtained by using French chalk and a piece of hard wood.

Clock wheels are polished with a piece of felt and rottenstone. They are subsequently soaped, washed and dried in sawdust. (=151=)

=186.= =To polish lever escape-wheel teeth.= The Lancashire escape-wheel makers employ a triangular frame carrying at its corners, (1) a cutter to slit the teeth, (2) a cutter to shape them, and (3) a revolving piece of hard leather of a section corresponding to the form of the space. This latter is charged with the finest glossing stuff, used dry, and the sides of the teeth of six wheels at a time are polished by revolving the disc in each of the spaces in turn. It is hardly necessary to observe that the operation is completed before the wheels are removed from the cutting engine.

=187.= =To polish sinks or oil-cups.= A piece of pegwood, rounded at the end, is used for this purpose, rotating it in a lathe; the watch plate or cock should be inclined in varying directions to the stick in order to remove scratches. If a very high polish is required it may be given by following with a stick, the end of which is covered with wash-leather charged with rouge.

TO POLISH STEEL.

=188.= The polishing must always be preceded by a very thorough smoothing, either with oilstone dust, fine emery, or coarse rouge. If any lines are left to be erased by means of fine rouge, the operation becomes tedious and is rarely successful. The oilstone dust is applied on an iron or copper polisher. When it is desired to preserve the angles sharp, at a shoulder for example, the polisher should be of steel.

When using diamantine an iron polisher, drawn out and flattened with a hammer, answers very well.

With fine rouge, a bronze or bell-metal polisher is preferable for shoulders; and, for flat surfaces, discs or large zinc or tin polishers, although glass is preferable to either of these.

After each operation with oilstone dust, coarse rouge, etc., the polisher, cork, etc., must be changed, and the object should be well cleaned—preferably by soaping; perfect cleanliness is essential to success.

Fine rouge or diamantine should be made into a thick paste with oil; a little is then taken on the polisher or glass and worked until quite dry. As the object is thus not smeared over, a black polish is more readily obtained, and the process gets on better if the surface is cleaned from time to time.

=189.= =To get a good black polish.= As just pointed out, this is mainly secured by using very little polishing material at once, in a very little liquid on either, the polisher or glass plate and drying up quickly. If the surface does not prove satisfactory at first, it will often be found that a final rapid and light application of dry diamantine or rouge on a piece of glass or pith will produce a brilliant black polish.

If operating on an axis or staff, polish as well as possible, first erasing the marks of the graver or file, and then, hold the ferrule between the fingers, rotate it with one hand and with the other rub the axis lengthwise with a pegwood stick charged with rouge or diamantine.

A rod will show a black polish if it be rubbed lengthwise with emery paper of gradually increasing fineness, oil being applied with the finest quality.

_To polish flat surfaces._ Place the object on a sound piece of cork covered with a clean rag and rub with, a long strip of ground glass.

_To polish a square shoulder._ Fix a rod in place of the T-rest of the turns, and set it in such a position that the polisher rests on this vertical rod when lying flat against the shoulder. Another and better method consists in cementing or otherwise fixing in the plane of the shoulder a brass disc of such dimensions that the polisher is constrained to remain flat.

_Observations._ The corner of the polisher that is used for polishing a shoulder should be neither right-angled nor too acute. In the first case it would round off the shoulder, and in the second it would become soon distorted and leave dull radial marks on the surface.

Diamantine should not be used for polishing the acting surfaces of pivots, the pallets of escapements, etc., since this material, as well as emery, is liable to leave particles embedded in the steel which occasion rapid wear.

CEMENT, WAX, RESIN, ETC.

=190.= The principal uses to which the watchmaker applies cement is for fixing objects in the lathe, pallet-stones in position, as well as locking and unlocking pallets, ruby-pins, etc.

The selection of a cement or wax is not a matter of indifference; fine sealing-wax causes objects to adhere firmly together, but many of the best workmen prefer refined shellac. Certain kinds of wax are too dry, the consequence being that a false stroke of the graver will often detach the piece; others are thick and soft, and are apt to heat rapidly under the action of the burnisher or polisher, so that the object is displaced. It is only by making a series of trials that the efficiency of the material can be ascertained. Some workers claim that a mixture of sealing-wax and shellac gives good results.

=191.= =Mode of applying cements.= When employing wax, resin, cement, etc., for uniting two objects, it is important to note that the mode in which it is applied has an important influence on its efficiency. The following observations on this point are due to M. Sibon, and the reader will be able to select those portions that have reference to his work.

When two objects are united by a cement, this will lose much of its value if unskillfully applied, and, in order to use it to the best advantage, the following practical rules should be observed.

1. The surfaces to be united must be quite clean.

2. The less cement, wax, etc., that is interposed between them, the better they will adhere. This is owing to the fact that with a thick layer the object has, at the junction, no more rigidity than that of the cement itself; as a rule this more fragile than the material it is employed to unite.

3. There should be perfect contact between the cement and the surfaces. With a view to securing this, the object must be first heated to a point such that the wax or cement cannot solidify without having first had time to effect a perfect union.

This remark is especially applicable when using sealing-wax, mixtures of resin, shellac, and similar materials. They will not adhere firmly unless the surfaces have been heated very nearly to the point of fusion of the cement. The sealing of letters offers an example in proof of this assertion. When the seal has been used several times in succession or been left too long on the wax so as to become hot, it will adhere and cause some inconvenience if further employed.

With hot melted glue, adhesion is best secured by friction or a moderate pressure.

Sealing-wax is excellent for uniting metal to glass or stone, providing they are sufficiently heated to melt it; for, if applied to cool surfaces, it will not adhere at all. By heating two pieces of glass or stoneware sufficiently to melt shellac, a small quantity will suffice to make them adhere firmly together; notwithstanding that every one has seen such joints, very few succeed in making them, for the simple reason that they do not recognize the necessity of heating a delicate piece of glass or china to the point which is essential for securing a good result.

In conclusion, the principal obstacles to adhesion are air and dirt. The first is always present; the second is due to accident or carelessness. All surfaces are covered with a thin layer of air that is very difficult to remove; its influence prevents highly polished metal from being moistened when immersed in water. So long as this layer of air is not displaced, the cement cannot adhere to the surface to which it is applied, because it cannot come into direct contact. The most effective agent for displacing this air is heat. Metals heated to about 75° C. (170° F.) are immediately moistened on being plunged into water, hence it follows that, as regards cements that are applied in a fused state, heat is the best means of bringing them into intimate contact with the surface.

We would add that, in addition to possessing this advantage, the application of heat also renders the surfaces more penetrable to the layer of cement, after the manner of soldering, and makes the interlocking of the molecules more perfect; this explains the greater degree of tenacity of a well made joint with only a thin layer of cement.

=192.= =To set in wax in the lathe.= Trace a series of concentric circles on the face of the chuck with a graver point, after turning it true: this will increase the adhesion of the cement. Then the flame of the spirit lamp is held under the rotating chuck and, when this is hot enough, its surface is covered with a layer of shellac or sealing-wax, and the object is held against it. Holding it in position with a piece of pegwood supported on the T-rest, the lamp is removed and the lathe kept rotating until the cement sets. The cooling can be hastened by applying a small moist sponge, but it should not set too suddenly.

If the object requires to be very exactly centered, its position must be insured while the cement is still soft by means of a long pegwood stick in its central hole. This stick is held in position until the cement sets, steadying it between two fingers close up to the chuck. The slightest eccentricity will be indicated by a motion of the free end of the stick.

If the object is round, and has no central hole, it must be centered by its circumference, holding the pegwood in front, or resting against a corner of a circular elevation or depression, as, for example, the collet of a wheel, or of a cylinder riveted to its balance, etc.

The beginner should make a number of trials; they will enable him both to acquire lightness of touch, and to recognize the proper degree of softness of the cement for centering, as well as its tenacity.

When it is essential that the two faces of the object be strictly parallel, a precaution is necessary; this consists in leaving on the face of the chuck a slightly projecting circular rim with a fine smooth edge, and of a diameter rather less than that of the object. By moving this latter backwards and forwards after applying it to the wax, and pressing it into close contact while cooling, the requisite parallelism will be secured.

=193.= =To fix a pallet-stone, etc., in position.= To fix a pallet-stone or an end-stone by means of shellac it is usual to place a small piece of the latter round the stone when in position and apply heat. But very often the lac spreads unevenly or swells up; and this, in addition to being unsightly, is apt to displace the stone. The inconvenience can be avoided as follows: The pallets are held in long sliding tongs, and, taking a piece of shellac, heat it and roll it into a cylinder between the fingers; again heat the extremity and draw it out into a fine thread. This thread will break off, leaving a point at the end of the lac. Now heat the tongs at a little distance from the pallets, testing the degree of heat by touching the tongs with the shellac. When it melts easily, lightly touch the two sides of the notch with it; a very thin layer can thus be spread over them, and the pallet-stone can then be placed in position and held until cold enough. The tongs will not lose the heat suddenly, so that the stone can easily be raised or lowered as required. The projecting particles of cement can be removed by a brass wire, filed to an angle and forming a scraper.

To fix an end-stone, the cap must be held by its edge in the sliding tongs, and shellac carefully applied around the edge of the hollow. It is advisable to hold the cap in a small tool formed of two parallel blades, as when reversed so as to press the stone on a flat surface, the shellac will spread over the end-stone, from which it will be removed with difficulty.

ENAMEL.

=194.= This name is applied to an opaque glass, with which various metallic compounds, such as oxide of tin, phosphate of lime, borax, etc., have been incorporated by fusion. The color, of course, varies with the substance so added.

Willis recommends the following as a good white enamel for dials: silver sand, 14 parts; borax, 10 parts; red lead, 18 parts; niter, 2 parts; oxide of tin, 12 parts; flint glass, four parts; and binoxide of manganese, 1-50th of a part. But a good deal of care is requisite, both in selecting the materials and preparing the enamel, in order to insure a pure color of any desired shade; it is, therefore, often desirable to purchase the enamel ready prepared.

In applying enamel, regard must be had to the relative dilatation of the metal to which it is applied, the two being so combined as to expand and contract together; otherwise there is danger of the enamel cracking, either at once or shortly after it has set.

Enamel may be applied to gold or copper. Associated with the latter, it forms the ordinary dials of watches and timepieces, and, with the former, it serves for making enameled gold dials or cases. The gold should be of 22 carat, the 2 carats of alloy consisting of equal parts of silver and copper. If the gold is of a higher standard, it will not adhere so well, and, if lower, there will be a further danger of melting the metal before the enamel is fused.

Silver is apt to cockle on the application of heat, and enamel applied to it presents a bubbly appearance.

=195.= =Application of enamel in the cold.= We are indebted for the following particulars to M. Fournier, of Dieppe, a well-known enamel maker:

There are two kinds of false enamel for application, when cold, to damaged dials.

The first, a mixture of white resin and white lead, melts like sealing-wax, which it closely resembles. It is advisable, when about to apply it, to gently heat the dial and the blade of a knife, and, with this, to cut a piece of enamel of the requisite size and lay it on the dial. The new enamel must project somewhat above the old. When cold, the surface is levelled by scraping, and a shining surface is at once produced by holding at a little distance from the flame of a spirit lamp. It is necessary to be very careful in conducting this operation, as the least excess of heat will burn the enamel and turn it yellow; it is, however, preferable to the following, although more difficult to apply, as it is harder and does not become dirty so soon.

The second false enamel contains white lead mixed with melted white wax. It is applied like a cement, neatly filling up the space, and afterwards rubbing with tissue paper to produce a shining surface; if rubbed with a knife blade or other steel implement its surface will be discolored.

PRECIOUS STONES.

=196.= The principal precious stones used in watches, chronometers and regulator clocks, in their order of hardness, are: diamond, ruby, sapphire, chrysolite.

A watchmaker, although he may not have had any previous experience of jewels, can easily ascertain their relative hardness by rubbing one against the other. The softer will be scratched by those that are harder, and the stone that can be marked by a file may be thrown aside as useless.

=197.= =Diamond.= We shall make a very brief reference to this stone, as it is not used except for the end-stones for balances for chronometers and high-class watches.

Splinters of diamond are employed for drilling materials of a less degree of hardness, and fragments fixed at the end of a rod are used for turning very hard steel; diamond dust is the principal material used for working precious stones, polishing, etc. (see articles =165= and =169=).

=198.= =Ruby.= This jewel, of a rich, velvetty, red color, exists in three principal varieties: oriental, spinel and balas rubies, which differ as regards their chemical composition.

From a jeweler’s point of view, the value of a ruby is enhanced by its rich color and transparency; but this is not the case in regard to its application in horology, for which hardness and capability of taking a high polish are mainly necessary.

The specific gravity of the three varieties is: oriental, 4.2; spinel, 3.7; balas, 3.6.

The first of these is the best, since it is the hardest, both taking a better polish in the first instance and retaining it for a longer period.

In comparison with the other varieties, its specific gravity is greater and it possesses a brighter color, but will often be found to be less transparent.

Spinel and balas rubies are frequently met with that are very beautiful to the eye, but their hardness is inferior to that of the sapphire and even of the chrysolite. They must be carefully excluded from all good work, for, either in consequence of the inferior hardness or the mode in which the oxide of iron, magnesia, etc., is combined, or of other causes, oil rapidly deteriorates in contact with them, and the moving parts, especially if they are of steel, soon show signs of wear. The rubies themselves also suffer, and it is by no means uncommon, especially in the case of the duplex escapement, to meet with such jewels quite rough and even pitted on their acting surfaces.

=199.= _False ruby._ In a certain class of watches, a variety of stones pass for rubies that are known to jewelers as rubicelle, rubace, rock ruby, Brazil, Siberian or Bohemian ruby, rose ruby, etc., the hardness of which is even less than that of rock crystal. Pivot-holes made of these imitations of the real ruby are worth less than plain brass settings.

=200.= =Sapphire.= The color of this stone, sometimes even milky, passes through all the shades of blue. Like the ruby, there are several varieties that differ appreciably in regard to hardness. The hardness of oriental sapphire is equal to that of oriental ruby; both consist of nearly pure alumina, colored by a little oxide of iron; their chemical composition thus being the same, they only differ in regard to color. It is, then, a great mistake on the part of watchmakers to prefer spinel or balas rubies in place of oriental sapphires.

The sapphire is more brittle than the ruby.

The other kinds of sapphire, such as water sapphires, are not true sapphires; they are soft and should never be used in horology. The density of the oriental sapphire is about 4.01, whereas that of other kinds is only 2.58.

=201.= =Chrysolite.= Under this name lapidaries include a variety of stones of yellow-green, apple-green with shades of yellow, and other colors.

That known as oriental chrysolite, which is the same as the oriental topaz, has a beautiful pale yellow color with shades of apple-green; it is the most highly esteemed. This stone has a sufficiently high degree of hardness for use in watchmaking, as it will scratch rock crystal. Its density varies from 3.73 to 3.00.

The other varieties, ordinary chrysolites, come very low in the scale of hardness. They can be scratched by quartz, rock crystal and even by the file, and are thus of no use for watches.

=202.= =Agate, Carnelian, Topaz.= Only the varieties of the stones already considered that are termed oriental can be used for the pivot-holes or the pallets of astronomical regulators, but for the escapements of the ordinary timepieces of commerce, such, for example, as the pallets of Brocot escapements, the topaz, agate or carnelian may be used. When of the hardest kind, and capable of receiving a high polish, they will very efficiently resist the friction of brass teeth. As to the softer kinds, they are inferior to hardened polished steel for pallets.

WORKING IN PRECIOUS STONES.

=203.= The methods adopted for working in the precious stones are in great parts kept secret by those who practise them; it is, however, well known to watchmakers that jewels are usually worked and polished with powdered diamond, and the following details will afford all the information necessary to enable the reader to make a jewel of any required form. Where not otherwise stated, the information is taken from a work published by N. Dumontier.[5]

=204.= =Tools for working jewels.= These are all of simple construction, and can be made by any watchmaker if, indeed, he has not them already to hand.

(1.) A small lathe arranged to receive chucks, fixed to the bench or in a vise, and driven by a foot-wheel. Its form resembles that shown in fig. 47.

(2.) Two circular laps of copper and one of tin about 2 inches in diameter and ⅛th inch thick; these present a flat face for grinding, smoothing and polishing the stones, and are adapted to the nose of the lathe.

(3.) A small barrel (that also screws into the nose of the lathe) with six brass covers, perforated at the center, on which to cement the jewel-holes, when enlarging, smoothing and polishing their holes.

(4.) A flat steel circular cutter half an inch in diameter, for slitting stones. Also two similar discs, one of copper and the other of tin, of the same size, and having sharp edges, are occasionally useful.

(5.) Two small laps, one of copper and one of tin, to smooth and polish cylindrical stones. These laps are mounted in place of the T-rest, or in the slide-rest, in such a manner that they can be rotated in a horizontal plane by a bow, in a manner sufficiently indicated by fig. 48.

(6.) Two chucks adapted to the lathe, on which to cement the jewels for drilling, turning and polishing.

(7.) A number of small broaches, spindles with concave and convex ends, etc., for smoothing and polishing jewel-holes, convex and concave surfaces.

There may also be added a small steel plug mortar for powdering the diamond (=169=), and a flat steel plate with a block for working up the powder.

=205.= =Selection of Stones.= This is of the first importance. By the aid of a powerful lens, or a microscope, ascertain that they contain no cracks, air cavities or black specks; avoid stones that are milky, preferring such as are marbled, and in which the directions of crystalization seem to cross one another, as they are the hardest. The hardness may be tested by trying them one against the other (=122=), but an experienced workman needs only to note the amount of resistance it offers to the operation of cutting on the lap. The density also affords a valuable means of determining the nature of stones. (See above notes on the several kinds.)

=206.= =To find the axis of crystallization of a stone.= It is well known that jewels differ from glass, in that they form crystals of certain definite forms; they are therefore termed “crystalline,” whereas glass is “vitreous.” If a jewel-hole is drilled in any direction other than the axis round which the crystal may be assumed to have been formed, there will be difficulty experienced in the drilling and polishing; the edges of the hole will become rough during the act of rounding them off, and the hardness will appear to be irregular. This point seems, however, to be ignored by the majority of jewel-hole makers, although the determination of the most suitable direction presents no difficulty.

Obtain, from any optician, two tourmaline plates cut parallel to their axis of crystallization and with their faces polished. Mount them in a light frame, parallel to each other, so that each can rotate independently of the other round the axis through their centers; it is convenient if a light spring tends to bring the plates together so that a stone can be held when placed between them. Or such an arrangement can be bought ready made at most opticians: it is known as a tourmaline polariscope. If this instrument be held up between the eye and a light, and one plate be rotated while the other remains stationary, it will be seen that the light becomes gradually greater or less according to the direction of rotation; and further, if the plates be good ones, a point will exist at which there is nearly total darkness.

To examine a stone, cut and polish on it two parallel faces approximately at right angles to the axis of crystallization; this can generally be roughly guessed at by inspection. Place it between the plates (when set at their darkest position), and not only will the light be in part restored but beautiful colored rings will be formed. If they are circular, the faces of the stone are at right angles to its axis; if not, incline it till the rings become so, and the axis will then coincide with that of the instrument. In case the rings are not observed at all, the stone must again be cut at right angles to the original direction, and the experiment repeated. If they still do not appear, the stone is unsuitable for drilling, but may be used for pallets, locking-stones, ruby-pins, etc.

The stones to be examined in this manner must be larger than those commonly met with, and if cylindrical rubies can be obtained they are to be preferred, as it is then only necessary to slice them across their axis.

It should perhaps be observed that these precautions can only be taken in making jewel-holes for the higher class of clocks, chronometers and watches. The cheaper class must of necessity be cut in such a manner as their figure may suggest.

=207.= =Making jewel-holes.= Having selected 20 or 30 stones of about the same height, cement them to a smooth brass or copper-plate, heated to melt the cement. Hold this plate in contact with a revolving copper lap in which the coarser quality of diamond powder (=169=) has been embedded by means of a hard steel block; the lap is moistened with water.

When one side of the stones is true, soften the cement and, after washing, place them in a vessel containing spirits of wine heated by a lamp. After doing the same to the plate, again cement the stones to it with the trued sides downwards, and grind the other faces until the desired thickness is arrived at. Clean the stones and smooth them on the brass lap charged in a similar manner with a finer quality of powder.

The stones are now ready for drilling. This may be done with diamond powder, or with the diamond drill, both of which methods will be explained.

=208.= _To drill with powder._ In drilling with powder, the stone is fixed with sealing-wax or shellac on a carrier that is adapted to the tool-holder of the slide-rest, this carrier being provided with a vertical slide, so that by the screws in three directions the stone can be accurately centered; it is, moreover, so arranged that the stone can be advanced to or from the drill by pressing with the finger axially. Drill a small hole in the center of the chuck and, after fixing a piece of steel in it that has been hardened and tempered to a greyish color, turn a point on it about twice the length of a pivot, to serve as a drill. This point must be slightly thinned backwards to prevent it from choking in the hole and its end should be flat, so as to retain the powder.

When the stone is exactly centered, place No. 2 diamond powder on the end of the drill, and press the stone gently against it, constantly releasing it from the drill for an instant at a time. The hole will be perforated in from 8 to 15 minutes, according to its depth, during which interval the powder should be renewed two or three times. Remove the stone and fix it on the barrel-chuck cover so as to turn true in the lathe; then turn out the oil-cup with a diamond graver of suitable form. See again that the stone is central, and re-center it if this be found necessary. This is done with the smooth conical end of a soft round broach, or a pegwood, a lamp being held under the chuck at the same time.

=209.= _To use the diamond drill._ Having centered the stone on the chuck, as explained in the preceding paragraph, set it in rotation and bring a sharp-pointed diamond graver against its center, pressing lightly and resting the handle on the =T=-rest; a minute central mark is thus made in the stone for maintaining the drill axial. Selecting a diamond drill of convenient diameter, moisten it in the mouth and present it to the mark, applying a gentle pressure, the amount of which can only be ascertained by practice. It is to be observed that a number of stones should, if possible, be drilled at the same time, for the hand is apt to lose the requisite knack, if only one or two are perforated at a time.

=210.= =Smoothing and Polishing.= When the hole is made through, remove the stone and invert it on the chuck. The diameter being less than that ultimately required, pass a brass broach charged with No. 3 powder through the hole, giving it a gentle axial motion while the stone revolves, and taking care to avoid pushing it so far forward as to lock in the stone, and holding it very lightly between finger and thumb. When sufficiently smooth, clean with rotten wood or soft bread, and treat it in a similar manner with a copper broach and No. 4 powder. Then again clean and use a tin broach and powder No. 5. Next, taking a small bone cone, smooth the angles of the holes; then use a copper wire with rounded end for smoothing the oil-cup (with powder No. 3); follow as explained for the hole with the finer degrees. Using a finely pointed pegwood that passes through the hole, _marry_ or round off the internal angle between the hole and oil-cup (the powder that remains in the hole being sufficient for this purpose) and do the same to the outer circumference of the cup with a copper spindle of somewhat larger diameter.

Round off external angles with a diamond graver followed by a copper polisher, the end of which is cup-shaped. The flat face of the stone is polished with a small copper disc and No. 4 powder, pressing it lightly with the finger at the same time that a circular movement is given to it; finish with No. 5 powder. Or the stone may be detached and the flat face polished by working on a ground glass plate, a pegwood point being passed into the hole to form a handle.

Re-set the stone, inverting it, on the chuck, centering it. The other side is then polished in the same manner, using such tools as its form may require.

Having thus completed the stone, examine it carefully with a powerful glass to ascertain that the hole is highly polished and the angles rounded off, etc. It is then ready for setting.

=211.= =Setting Jewel-holes.= Whether it be a plate, cock or bushing in which the stone is to be set, the piece must always be cemented to a chuck and the hole accurately centered. Turn it out to a depth corresponding to the thickness of stone, and make a circular groove round the hole thus made with a round-pointed graver, only leaving a very thin fillet of metal on the inside. The stone should fit easily in the hole, but without play, and should pass in to such a depth that its surface is slightly below that of the plate, etc., when there is an end-stone; in other cases it must, of course, often depend on the end-shake to be obtained. At the same time it appears desirable that it always should be slightly below.

Clean out the setting and place a small quantity of oil in it to prevent the stone from flying out when made to rotate; or it may be rendered still more safe by a pointed pegwood held in the hand. The stone is fixed in position with a small conical burnisher (as, for example, the point of a round broach) very carefully polished, so as to avoid all abrading action; if an excess of metal is forced over the surface of the stone, it is removed with a graver. The surface of the brass is finally smoothed with pith or pegwood, and tripoli in oil, followed with polishing rouge in spirits of wine.

English jewel-setters often do not turn the groove, but leave a projecting edge round the hole, which is pressed on to the stone with a burnisher.

=212.= =To Make End-stones.= The details already given will enable any intelligent workman to make end-stones. If one of diamond in a brass or steel setting is required, take a small rose-cut stone, turn out a hole in the chuck to receive it, and, after cementing in position, turn off the corners with a diamond graver so as to be able to set it.

For making end-stones of ruby, sapphire or chrysolite, flatten a face, using the laps Nos. 1, 2, and 3 in succession, or a plate of ground glass. Then cement with the flat face towards the chuck, and turn to the requisite form with a diamond graver. Polish with the cup-ended brass and copper spindles, and set, if requisite, in the same manner as a jewel-hole.

=213.= =To make pallets, unlocking pallets, etc.= This may be done on the lap, or by using files of soft steel, copper and tin. In the first case the stones are roughed out while held by the hand, and the required form is given them while holding them in a small carrier that fits into the T-rest support, but the forms of such stones are so various that no special details can be here given. The diamond powder of different degrees of fineness is used, as in making jewel-holes.

=214.= =To make semi-cylindrical locking stones, ruby-pins, etc.= The stone must first be made approximately cylindrical on the lap No. 1, so that it may be turned with the diamond graver. Drill a hole in the chuck, cement the stone in it and turn it in this manner. When true and of the requisite length and diameter, round off the outer end and smooth with a cup-ended spindle, then polish with powders 3 and 4 successively. Round off the sharp corner with a cup of rather greater curvature. The cylindrical surface is polished by means of a small lap carried on a vertical spindle in a frame fixed in the T-rest support, and caused to rotate rapidly with a bow, the lathe-head also revolving at the same time (=179=). The lap-carriage should have a vertical screw adjustment so that it may be brought just into contact with the stone; it is supplied with the several degrees of powder in turn. Now drill a hole in another chuck of the diameter of this cylinder, fix it in position and finish off the opposite end.

To form the flat face along the axis of the stone it is cemented to a support in place of the =T=-rest and brought against the revolving lap in the lathe; or the same result may be attained by using a brass file.

=215.= =To make a duplex roller.= At the present day this operation so rarely has to be done that only a few words can be devoted to its consideration.

Very pure rubies must be selected, and the hole drilled as explained in =209=; if the drill is too short it must be introduced at opposite ends, and the two holes made to meet. After smoothing the surface, the notch is cut with the thin steel cutter referred to in article =204=, the roller being cemented to a support that replaces the T-rest. When the steel disc charged with powder No. 4 is revolving very rapidly, advance the roller under it by a screw. The notch is polished by a small copper file of suitable form, and its corners rounded off by a tin one of square section, one edge of which enters the notch.

=216.= =To mount diamond drills and gravers.= Drill a hole or file a notch in the end of a piece of brass wire to correspond with the fragment of diamond; heat the end in a spirit lamp and lay on it a piece of good sealing-wax or shellac. When this commences to melt, set the diamond in position and leave the whole to cool. Diamond drills are very commonly mounted at the end of a pin that has had its point filed off; mark a point on the end with a graver and drill the hole, which should be very shallow. Holding the pin in a pin-vise with its point projecting about 1-10th inch, heat the vise in a lamp, and proceed as above explained.

FOOTNOTES:

[4] The theoretical density of an alloy, on the assumption that in alloying the metals do not contract or expand, is obtained by dividing the percentage proportion of each constituent metal by its density, adding the products so obtained together, and dividing their sum into 100.

[5] _L’art de travailler les Pierres precieuses a l’usage de l’Horlogerie et de l’Optique._ Paris. 1843.